1. Field of the Invention
The present invention relates to a flash device and a reflector for a flash discharge tube. More particularly, the present invention relates to a flash device and a reflector for a flash discharge tube used in a lens-fitted photo film unit or a compact camera.
2. Description Related to the Prior Art
A lens-fitted photo film unit is commercially available and widely used, which has a housing incorporating an exposure-taking mechanism of a simple structure, and is preloaded with unexposed photo film. There are various types of lens-fitted photo film units, one of which incorporates an electronic flash device for the purpose of taking photographs indoors or at night. The flash device to be built in the lens-fitted photo film unit has a simple structure to decrease the cost of the lens-fitted photo film unit, and consists of a flash unit in which a printed circuit board is used to mount electrical parts constituting a flash emitter of a flash circuit.
The flash emitter is structurally constituted by a flash discharge tube, a reflector, a diffuser plate and a reflector case. The flash discharge tube emits flash light upon discharging operation of electric charge stored in a main capacitor. The reflector is curved for reflecting the flash light emitted by the flash discharge tube toward the front in a predetermined illuminating pattern. The reflector case contains and supports those elements. As is well-known in the art, the flash discharge tube consists of a flash tube body of glass enclosing xenon (Xe) gas. For flash emission of the flash discharge tube, the main capacitor has been charged to apply predetermined voltage to terminals of the flash discharge tube. Trigger voltage, for example as high as 4 kV, is generated by a trigger transformer, and applied to the outer surface of the flash tube body for trigger current to flow to it, so that the xenon gas is ionized.
To supply the flash discharge tube with trigger current, it is known to wind an electrically conductive wire directly on the flash tube body to apply the trigger voltage to the flash tube body through the wire. Or the flash tube body is kept in contact with the inside of the reflector electrically conductive. The trigger voltage is applied to the reflector and then to the flash tube body for triggering the flash emitting operation.
To apply the trigger voltage to the reflector, a lead line is connected between a trigger output terminal of the trigger transformer and the reflector. Or a trigger segment of metal is used to contact the reflector for application of the trigger voltage from the trigger transformer. The use of the lead line is less advantageous, because parts of the flash device cannot be very easily assembled in an automated manner. Thus the trigger segment is more widely used.
It is general in the flash device that the trigger segment for transmitting the trigger current has an end soldered on to the trigger output terminal of a secondary winding of the trigger transformer.
In most of widely used flash devices, the reflector, as viewed in a cross section, has a shape of an elliptical arc as a curved reflective surface, to regulate illumination adequately. Also there are known reflective surfaces defined by a hyperbolic curve, a parabolic curve or other suitable functional curves.
When the trigger segment is used as described above, the trigger segment is caused to push the reflector with sufficient pressure for ensure application of trigger voltage to the reflector. However the pressure of the trigger segment is likely to deform the reflector in such a manner that an illuminating pattern of the flash light at a distance of several meters becomes different from an illuminating pattern initially expected for the flash device. Such an unexpected illuminating pattern of flash light causes an irregularity in exposure of a photograph taken with the flash light.
The above-described soldering process of the metal plate or lead line to the trigger output terminal of the secondary winding of the trigger transformer is much complicated and requires long time of assembly. It is difficult to decrease the manufacturing cost or to increase the productivity of the flash device. Also in view of administration of the manufacture, the soldering process must be inspected in a periodical manner. Soldering itself has a problem of much use of electric power and much metal as solder.
The reflector having the above-described curved reflective surface defined by the elliptical arc has a difficulty in controlling rays incident on an illuminating region. It is impossible to increase light condensing efficiency considerably, which is defined as a ratio of an amount of rays incident on a photographic field to a total amount of rays emitted by the flash discharge tube. In the type of the reflector defined by the functional curves, the light condensing efficiency would be increased by use of a protector operating as a Fresnel lens, which is transparent and covers the front of the reflector. However this construction requires a considerable back-to-front space of the flash emitter, to enlarge the size of the flash device. Also the protector as a Fresnel lens requires a complicated process to be molded, and increases its manufacturing cost.